1. Field of the Invention
The present invention relates to a bolt with a magnet and designed to be screwed-in into a lubricant-containing housing, e.g., of a hand-driven tool, and including a head portion having rotation-transmitting surfaces, and a shank portion extending from the head portion and having an outer thread and a recess for form-locking receiving the magnet.
2. Description of the Prior Art
Hand-driven tools such as, e.g., chisel tools, have a drive and a percussion mechanism. Both the drive and the percussion mechanism have mechanically cooperating metallic components. With the cooperating metallic components, despite lubrication, metallic abrasion or dust is formed which becomes distributed in the lubricant. The metallic abrasion or dust contained in the lubricant reaches the bearings and toothings and leads to excessive wear and premature damage of the ball bearings and toothings.
U.S. Pat. No. 4,810,148 discloses a drain bolt for collecting metallic dust accumulating in a gear housing. The drain bolt has a magnet and is screwed-in into the housing. The bolt has a head portion and a shank portion, with the head portion extending radially beyond the shank portion. The shank portion has an outer thread and a recess formed at the free end of the shank portion. The rotation-transmitting surfaces of the head portion are defined by an outer contour of the head portion having a shape of a hexagon engageable by a wrench.
The magnet projects into the recess and has a portion projecting beyond the free end of the shank portion. The portion of the magnet, which projects beyond the free end of the shank portion, has a length exceeding the entire length of the bolt. Because of its large length, the projecting portion of the magnet extends deep into the inner space of the gear housing and is washed around with the circulating lubricant. The metallic dust distributed in the lubricant is attracted to the magnet and is retained on the free end and on the circumference of the magnet.
The drawback of the drain bolt disclosed in U.S. Pat. No. 4,810,148 consist in that the magnet can hit the thread when the bold is removed, so that a portion of the metal dust, which was collected on the magnet circumference, would be stripped by the thread of the housing and would accumulate there. During a subsequent screw-in of the bolt, the metallic dust or abrasion, which accumulated on the housing thread, can lead to the distortion of the thread connection between the bolt and the housing or would lead to seal leakage in the region of the thread connection. A further drawback of the known drain bolt consists in that the housing, in order to prevent a collision between the elongate portion of the magnet and the movable components of the drive, should have an additional space for receiving the projecting portion of the magnet. This leads to an increased overall dimension of the housing.
Accordingly, an object of the invention is to provide a bolt with a magnet capable of collecting a large amount of metallic abrasion or dust, without the metallic dust being able to be deposited on the housing thread and without the magnet having portions which could collide with the movable parts in the housing.